METHOD FOR MAPPING A PARTIAL LETHAL-FACTOR LOCUS ON A MOLECULAR-MARKER LINKAGE MAP OF A BACKCROSS AND DOUBLED-HAPLOID POPULATION

Distorted segregation has been repeatedly observed in various plant sp ecies in molecular-marker linkage mapping where distant crosses were m ade. It may be caused by a partial lethal-factor acting in the filial generations. A method is presented for estimating the recombination va lues between a partial lethal-factor locus and a linked molecular mark er and the relative viability or fertilization ability of zygotes or g ametes, respectively affected by the partial lethal factor in backcros s (BC) and doubled-haploid (DH) populations using the maximum-likeliho od method associated with the expectation maximization (EM) algorithm. The method was applied to segregation data of molecular markers for a population of 150 DH lines developed from the 'Steptoe' x 'Morex' cro ss in barley. The presence of a partial lethal-factor locus, located o n chromosome 4, causing partial selection was suggested. This locus wa s tightly linked to the ABG500B marker, and the chance of fertilizatio n of female gametes possessing the partial lethal factor was, on avera ge, 59.8% that of a normal one. Two additional partial lethal factors were found on chromosome 5.